Bird watching - Feed them fresh fruit - Baltimore Orioles love oranges and Cardinals love grapes. Orioles love grape jelly too and if you put out either one, woodpeckers really like them too. Butterflies like them too.
could do bug obstacle course DIY American Ninja Warrior Backyard Obstacle Course - Five different elements. Build and re-build this obstacle course, and then it breaks down for storage. Storage ideas in the post.